1. Field of the Invention
The present invention relates to the debarking tooth of a debarking machine for debarking the bark of trees and other bark covered growth, hereinafter referred to as "wood", and, more particularly, to an improvement of the attachment structure of a platform and a blade tip plate, which constitute a debarking tooth, in order to attach the blade tip plate to the platform more securely.
2. Description of the Related Art
An example of a debarking machine is disclosed in, for example, Examined Japanese Patent Publication No. Hei 4-20761. Each debarking tooth of the disclosed debarking machine has a structure as shown in FIGS. 21 to 23. The debarking tooth 201 comprises a platform 203 and a blade tip plate 205 which is securely joined to the platform 203 in a detachable manner. The platform 203 is secured to the outer surface of a rotary member 207. The rotary member 207 is rotatably positioned in a wood container (not shown) at the lower portion thereof. A engage projection 209 is protrusively provided at the joined surface of the platform 203 where the blade tip plate 205 is attached, as shown in FIG. 22. Formed in the joined surface of the blade tip plate 205 is an engage recess 211 which is to engage with the engage projection 209. The fitting allowance of the engage projection 209 with the engage recess 211 is set relatively large. This is because if the fitting allowance, is set too small, it may interfere with easy engagement of the projection 209 and the recess 211 with each other, thus making the assembling work difficult.
A plurality of tooth portions (four tooth portions in this case) 205a protrude from the upper portion of the blade tip plate 205 in FIG. 21. Those tooth portions 205a provide the desired debarking performance. A separate engage member 215 is securely welded to the rear one of both lengthwise ends of the platform 203 in the rotational direction of the rotary member 207. When the debarking tooth 201 is in use, a load acts toward the rear end of the platform 203 in the rotational direction of the rotary member 207 and this load is received by the engage member 215.
In securely attaching the thus constituted blade tip plate 205 to the platform 203, first, the engage projection 209 of the platform 203 is engaged with the engage recess 211 of the blade tip plate 205. This engagement is conducted mainly for the positioning purpose. Under this situation, fixing bolts 217 are fastened toward the platform 203 from the blade tip plate 205 at three sections. As a result, the blade tip plate 205 is securely attached to the platform 203.
A plurality of debarking teeth 201 with the above-described structure are attached to the outer surface of the rotary member 207 to debark the bark of loaded wood as the rotary member 207 rotates.
The blade tip plate 205 as shown in FIG. 21 is used for non-frozen wood. Further, various kinds of blade tip plates 205 whose tooth portions 205a have different shapes as shown in FIGS. 24A, 24B and 24C are used in accordance with the types of wood (hard wood and soft wood) and a change in the degree of wood's dryness or the like. The blade tip plate 205 as shown in FIG. 23 is used for frozen wood.
The above-described conventional structure has the following problems.
A large horizontal load (the load which acts from the direction perpendicular to the sheet surface in FIG. 20) acts on the three fixing bolts 217 which securely attach the blade tip plate 205 to the platform 203. This deteriorates the securing performance of the fixing bolts 217, and may thus loosen the attachment of the blade tip plate 205 to the platform 203 or may separate the blade tip plate 205 from the platform 203 in the worst case. This problem will be discussed more specifically. As already described, the blade tip plate 205 is designed to permit the engagement of the engage recess 211 with the engage projection 209 of the platform 203. This engagement structure is mainly for positioning of the blade tip plate 205 and the platform 203, but is not designed to receive the horizontal load. Therefore, a large horizontal load acts on the three fixing bolts 217.
To cope with the action of such a horizontal load, the diameter of the fixing bolt 217 may be increased or the number of the fixing bolts 217 may be increased. The width of the debarking tooth 201 is restricted, so that if the number of the fixing bolts 217 is increased under such restriction, the mechanical strength of the debarking tooth 201 itself is impaired. Likewise, the increase in the diameter of the fixing bolt 217 is limited from the view point of keeping the mechanical strength of the debarking tooth 201.
The aforementioned problem occurs even if the diameter of the fixing bolt 217 is increased or the number of the fixing bolts 217 is increased within the range where the mechanical strength of the debarking tooth 201 can be maintained.
Another possible problem is the penetration of a foreign matter between the blade tip plate 205 and the platform 203 (particularly between their joined surfaces), thus impairing the firm attachment of the blade tip plate 205 to the platform 203. As mentioned earlier, a certain degree of a fitting allowance (a certain degree of clearance) is given to the engage recess 211 of the blade tip plate 205 and the engage projection 209 of the platform 203. With such a slight clearance, a foreign matter may enter between the blade tip plate 205 and the platform 203 at the time of assembling them or while this debarking tooth 201 is in use. The penetrated foreign matter may deteriorate the firm attachment of the blade tip plate 205 to the platform 203.